Question: My son is insisting that I can send him postcards to his name and 9-digit ZIP code, with no street address included. I don’t believe him. What’s the story and how do ZIP+4 ZIP codes work?

Anyone know of a Zip+4 mailing address lookup service that's publicly available as a web service? I need to provide the complete zip codes for a mailing list that I'm working on. I want to be able to ...